Infants with congenital heart disease frequently experience failure to thrive. Several factors are thought to contribute to the growth retardation of these infants, including increased resting metabolic rate, increased energy expenditure in physical activity, and decreased nutritional intake. The purpose of this study is to compare the total daily energy expenditure of 3-4 month old infants with moderate to large ventricular septal defects with those of healthy control infants in order to determine if there is an increase in the total daily energy expenditure in infants with congenital heart disease with significant left-to-right shunting. The right heart pressures, quantity of the left-to-right shunt, and size of the ventricular septal defect will be measured in order to assess any possible association between these factors and variations in energy requirements or severity of failure to thrive that may occur in the group of infants with heart disease.